The present invention relates generally to the field of plant molecular biology, plant transformation, and plant breeding. More specifically, the invention relates to insect resistant transgenic corn plants comprising a novel transgenic genotype and to methods of detecting the presence of nucleic acids that are unique to the transgenic corn plants in a sample and compositions thereof.
Plant pests are a major factor in the loss of the world's important agricultural crops. About $8 billion are lost every year in the U.S. alone due to infestations of non-mammalian pests including insects. In addition to losses in field crops, insect pests are also a burden to vegetable and fruit growers, to producers of ornamental flowers, and to home gardeners.
Insect pests are mainly controlled by intensive applications of chemical pesticides, which are active through inhibition of insect growth, prevention of insect feeding or reproduction, or cause death. Good insect control can thus be reached, but these chemicals can sometimes also affect other, beneficial insects. Another problem resulting from the wide use of chemical pesticides is the appearance of resistant insect varieties. This has been partially alleviated by various resistance management practices, but there is an increasing need for alternative pest control agents. Biological pest control agents, such as Bacillus thuringiensis (Bt) strains expressing pesticidal toxins like δ-endotoxins, have also been applied to crop plants with satisfactory results, offering an alternative or compliment to chemical pesticides. The genes coding for some of these δ-endotoxins have been isolated and their expression in heterologous hosts have been shown to provide another tool for the control of economically important insect pests. In particular, the expression of Bt δ-endotoxins has provided efficient protection against selected insect pests, and transgenic plants expressing such toxins have been commercialized, allowing farmers to reduce applications of chemical insect control agents.
Another family of insecticidal proteins produced by Bacillus species during the vegetative stage of growth (vegetative insecticidal proteins (Vip)) has also been identified. U.S. Pat. Nos. 5,877,012, 6,107,279, and 6,137,033, herein incorporated by reference, describe a new class of insecticidal proteins called Vip3. Other disclosures, including WO 98/18932, WO 98/33991, WO 98/00546, and WO 99/57282, have also now identified homologues of the Vip3 class of proteins. Vip3 coding sequences encode approximately 88 kDa proteins that possess insecticidal activity against a wide spectrum of lepidopteran pests, including, but not limited to, black cutworm (BCW, Agrois ipsilon), fall armyworm (FAW, Spodoptera frugiperda), tobacco budworm (TBW, Heliothis virescens), sugarcane borer, (SCB, Diatraca saccharalis), lesser cornstalk borer (LCB, Flasmopalpus lignosellus), and corn earworm (CEW, Helicoverpa zea), and when expressed in transgenic plants, for example corn (Zea mays), confer protection to the plant from insect feeding damage.
Present plant transformation methods generally lead to the random integration of transgenes like vip3 into a host-plant genome. This random insertion of introduced DNA into the plant's genome can be lethal if the foreign DNA happens to insert into, and thus mutate, a critically important native gene. In addition, even if a random insertion event does not impair the functioning of a host cell gene, the expression of an inserted foreign gene may be influenced by “position effects” caused by the surrounding genomic DNA. In some cases, the gene is inserted into sites where the position effects are strong enough to prevent the synthesis of an effective amount of product from the introduced gene. For example, it has been observed in plants that there may be wide variations in levels of expression of a heterologous gene introduced into a plant's chromosome among individually selected events. There may also be differences in spatial or temporal patterns of expression, for example, differences in the relative expression of a transgene in various plant tissues, that may not correspond to the patterns expected from transcriptional regulatory elements present in the introduced gene construct. In other instances, overproduction of the gene product has deleterious effects on the cell. Because of these potential problems, it is common to produce hundreds of different events and screen those events for a single event that has desired transgene expression patterns and levels for commercial purposes. However, once a commercially viable site within the plant's genome is identified it would be advantageous to target genes of interest to that non-detrimental site.
Several methods for the targeted insertion of a nucleotide sequence of interest into a specific chromosomal site within a plant cell have been described. Site-specific recombination systems have been identified in several prokaryotic and lower eukaryotic organisms. Such systems typically comprise one or more proteins that recognize two copies of a specific nucleotide sequence, cleave and ligate those nucleotide sequences, and thereby provide a precise, site-specific exchange of genetic information. Several site-specific recombinases are known in the art. These include, but are not limited to, e.g., the bacteriophage P1 Cre/lox system (Austin et al. (1981) Cell 25: 729-736), the R/RS recombinase system from the pSR1 plasmid of the yeast Zygosaccharomyces rouxii (Araki et al. (1985) J. Mol. Biol. 182: 191-203), the Gin/gix system of phage Mu (Maeser and Kahlmann (1991) Mol. Gen. Genet. 230: 170-176), the FLP/FRT recombinase system from the 2.mu.m plasmid of the yeast Saccharomyces cerevisiae (Broach et al. (1982) Cell 29: 227-234), and the Int recombinase from bacteriophage Lambda (Landy (1989) Annu. Rev. Biochem. 58: 912-949; Landy (1993) Curr. Opin. Genet. Dev. 3: 699-707; Lorbach et al. (2000) J. Mol. Biol. 296: 1175-1181; and WO 01/16345). One particularly useful site-specific targeting approach, disclosed in US Patent Application Publication No. 2006/0130179, herein incorporated by reference, uses lambda integrase mediated recombination. The method comprises introducing into a plant cell a target nucleotide sequence comprising a first Integrase Recognition Site; introducing into the plant cell a donor nucleotide sequence comprising a second Integrase Recognition Site; and introducing into the plant cell an Integrase or Integrase complex. Another useful site-specific targeting approach is disclosed in US Patent Application Publication No. 2006/0253918, herein incorporated by reference, which uses homologous recombination to integrate one or more genes (gene stacking) at specific locations in the genome.
An event that has desired levels or patterns of transgene expression is useful for introgressing the transgene into other genetic backgrounds by sexual out-crossing using conventional breeding methods. Progeny of such crosses maintain the transgene expression characteristics of the original transformant. This strategy is used to ensure reliable gene expression in a number of varieties that are well adapted to local growing conditions. It would also be advantageous to be able to detect the presence of a particular event in order to determine whether progeny of a sexual cross contain a transgene of interest. In addition, a method for detecting a particular event would be helpful for complying with regulations requiring the pre-market approval and labeling of foods derived from recombinant crop plants, for example. It is possible to detect the presence of a transgene by any well-known nucleic acid detection method including but not limited to thermal amplification (polymerase chain reaction (PCR)) using polynucleotide primers or DNA hybridization using nucleic acid probes. Typically, for the sake of simplicity and uniformity of reagents and methodologies for use in detecting a particular DNA construct that has been used for transforming various plant varieties, these detection methods generally focus on frequently used genetic elements, for example, promoters, terminators, and marker genes, because for many DNA constructs, the coding sequence region is interchangeable. As a result, such methods may not be useful for discriminating between constructs that differ only with reference to the coding sequence. In addition, such methods may not be useful for discriminating between different events, particularly those produced using the same DNA construct unless the sequence of chromosomal DNA adjacent to the inserted heterologous DNA (“flanking DNA”) is known.
For the foregoing reasons, there is a need for insect resistant transgenic corn events comprising novel nucleic acid sequences which are unique to the transgenic corn event, useful for identifying the transgenic corn event and for detecting nucleic acids from the transgenic corn event in a biological sample, as well as kits comprising the reagents necessary for use in detecting these nucleic acids in a biological sample. There is a further need to provide specific target sites within the maize genome to allow for targeting and control of insertion of nucleotide sequences to be integrated into the corn genome.